Therapeutic tables, or beds, of the type which have a frame, a patient support mounted to the frame for periodic, reciprocal rocking or tilting movement, a power drive train for such movement and a controller for the drive train are well known. Examples of such tables are shown in international application No. PCT/US83/01298, published Mar. 14, 1985, under Publication No. WO 85/0097, and the patents cited therein.
Electronic controllers for such tables are shown both in the aforementioned, patent application and in the following U.S. Pat. Nos.: 3,247,528 of Swenson et al.; 3,793,652 of Linehan et al.; 4,277,857 of Szehaug; and 4,194,499 of Donnelly, Jr.
In the table of the aforementioned patent application, the patient support is mounted to the frame for pivotal movement around its elongated axis in a side-to-side periodic tilting action. In addition, its pitch, or Trandelenberg angle, is adjustable to permit tilting of the bed around an axis transverse to its elongate axis. This type of Trandelenberg positioning is also shown in the above U.S. patents.
An important consideration in the beneficial use of such therapeutic tables is the reliability of control. In the controller of the aforementioned patent application, the amount of movement was controlled via the timing that drive powered was applied. It was assumed the drive would operate at a fixed rate and thus if it operated for a known time, the degree of tilt could be controlled. While this approach functions satisfactorily, it, of course, lacks the positive and absolute control that can be achieved only by direct measurement of the tilt angles during the periodic movement of the patient support.
In any event, the degree of maximum tilt on either side of a horizontal reference should be adjustable independently of one another. While independent control of the degree of tilt to both the left and the right of horizontal was achieved with the controller of the aforementioned patent application, such control again relied upon the timers and asumptions concerning drive speed.
When the movements of the patient support relative to the frame of the therapeutic table are powered by means such as electric motors, it is imperative from both a safety and an equipment protection viewpoint to minimize the continuation of drive power in the event of a jam condition. Such a jam condition could result from other hospital equipment interfering with the movement of the patient support. While the use of slip clutches and emergency clutch release mechanisms are known, these approaches do not function to automatically correct the jammed condition, although they may alleviate it. Instead, they depend upon operator involvement to correct the jammed condition.
Another difficulty with known therapeutic tables is that the setting of tilt limits has often been cumbersome or awkward and displays and other feedback information to the operator have been less than adequate to facilitate easy set-up operation and monitoring.